Mass spectrum analysis
Mass spectral interpretation is the systematic analysis of mass spectra for molecule identification. It is most often used for the identification of organic compounds from electron ionization mass spectrometry. Organic chemists obtain mass spectra of chemical compounds as part of structure elucidation and the analysis is part of many organic chemistry curricula.
Electron ionization (EI) is a type of mass spectrometer ion source in which a beam of electrons interacts with a gas phase molecule M to form an ion according to
with a molecular ion . The superscript "+" indicates the ion charge and the superscript "•" indicates an unpaired electron of the radical ion. The energy of the electron beam is typically 70 electronvolts and the ionization process typically produces extensive fragmentation of the chemical bonds of the molecule.
The peak in the mass spectrum with the greatest intensity is called the base peak. The molecular ion is often, but not always, the base peak.
Identification of the molecular ion can be difficult. Examining organic compounds, the relative intensity of the molecular ion peak diminishes with branching and with increasing mass in a homologous series. In the spectrum for toluene for example, the molecular ion peak is located at 92 m/z corresponding to its molecular mass. Molecular ion peaks are also often preceded by a M-1 or M-2 peak resulting from loss of a hydrogen radical or dihydrogen.
...
Wikipedia